WO2009084719A1 - Membrane microporeuse, procédé pour produire cette membrane et utilisation de cette membrane - Google Patents

Membrane microporeuse, procédé pour produire cette membrane et utilisation de cette membrane Download PDF

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Publication number
WO2009084719A1
WO2009084719A1 PCT/JP2008/073936 JP2008073936W WO2009084719A1 WO 2009084719 A1 WO2009084719 A1 WO 2009084719A1 JP 2008073936 W JP2008073936 W JP 2008073936W WO 2009084719 A1 WO2009084719 A1 WO 2009084719A1
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Prior art keywords
membrane
polyethylene
temperature
polypropylene
heat
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PCT/JP2008/073936
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English (en)
Inventor
Kotaro Takita
Norimitsu Kaimai
Yoichi Matsuda
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Tonen Chemical Corporation
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Priority to US12/744,030 priority Critical patent/US20100316902A1/en
Publication of WO2009084719A1 publication Critical patent/WO2009084719A1/fr

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/403—Manufacturing processes of separators, membranes or diaphragms
    • H01M50/406—Moulding; Embossing; Cutting
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/409—Separators, membranes or diaphragms characterised by the material
    • H01M50/411—Organic material
    • H01M50/414—Synthetic resins, e.g. thermoplastics or thermosetting resins
    • H01M50/417—Polyolefins
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/60—Other road transportation technologies with climate change mitigation effect
    • Y02T10/70—Energy storage systems for electromobility, e.g. batteries

Definitions

  • MICROPOROUS MEMBRANE PROCESS FOR PRODUCING SUCH A MEMBRANE AND THE USE OF SUCH A MEMBRANE
  • the invention relates to a microporous membrane having an improved balance of important properties such as melt down temperature and thickness fluctuations.
  • the invention also relates to a system and method for producing such a membrane, the use of such a membrane as a battery separator film, batteries containing such a membrane, and the use of such batteries as a power source in, e.g., electric and hybrid electric vehicles.
  • Microporous polyolef ⁇ n membranes are useful as separators for primary batteries and secondary batteries such as lithium ion secondary batteries, lithium- polymer secondary batteries, nickel-hydrogen secondary batteries, nickel-cadmium secondary batteries, nickel-zinc secondary batteries, silver-zinc secondary batteries, etc.
  • the microporous polyolefin membrane When used as a battery separator, particularly as a lithium ion battery separator, the membrane's performance significantly affects the properties, productivity and safety of the battery. Accordingly, the microporous polyolefin membrane should have suitably well-balanced permeability, mechanical properties, dimensional stability, shutdown properties, meltdown properties, etc.
  • well-balanced means that the optimization of one of these characteristics does not result in a significant degradation in another.
  • the batteries it is desirable for the batteries to have a relatively low shutdown temperature and a relatively high meltdown temperature for improved battery safety, particularly for batteries exposed to high temperatures under operating conditions. Consistent dimensional properties, such as film thickness, are essential to high performing films. A separator with high mechanical strength is desirable for improved battery assembly and fabrication, and for improved durability.
  • the optimization of material compositions, casting and stretching conditions, heat treatment conditions, etc. have been proposed to improve the properties of microporous polyolefin membranes.
  • microporous polyolefin membranes consisting essentially of polyethylene (i.e., they contain polyethylene only with no significant presence of other species) have relatively low meltdown temperatures. Accordingly, proposals have been made to provide microporous polyolefin membranes made from mixed resins of polyethylene and polypropylene, and multi-layer, microporous polyolefin membranes having polyethylene layers and polypropylene layers in order to increase meltdown temperature. The use of these mixed resins can make the production of films having consistent dimensional properties, such as film thickness, all the more difficult. [0005] U.S. Patent No.
  • 4,734,196 proposes a microporous membrane of ultra-high- molecular-weight alpha-olefin polymer having a weight-average molecular weight greater than 5 x 10 5 , the microporous membrane having through holes 0.01 to 1 micrometer in average pore size, with a void ratio from 30 to 90% and being oriented such that the linear draw ratio in one axis is greater than two and the linear draw ratio is greater than ten.
  • the microporous membrane is obtained by forming a gel-like object from a solution of an alpha-olefin polymer having a weight-average molecular weight greater than 5 x 10 5 , removing at least 10 wt.% of the solvent contained in the gel-like object so that the gel-like object contains 10 to 90 wt.% of alpha-olefin polymer, orientating the gel-like object at a temperature lower than that which is 10°C above the melting point of the alpha-olefin polymer, and removing the residual solvent from the orientated product.
  • a film is produced from the orientated product by pressing the orientated product at a temperature lower than that of the melting point of the alpha- olefin polymer.
  • U.S. Patent Publication No. 2007/0012617 proposes a method for producing a microporous thermoplastic resin membrane comprising the steps of extruding a solution obtained by melt-blending a thermoplastic resin and a membrane-forming solvent through a die, cooling an extrudate to form a gel-like molding, removing the membrane-forming solvent from the gel-like molding by a washing solvent, and removing the washing solvent, the washing solvent having (a) a surface tension of 24 mN/m or less at a temperature of 25°C, (b) a boiling point of 100°C or lower at the atmospheric pressure, and (c) a solubility of 600 ppm (on a mass basis) or less in water at a temperature of 16°C; and the washing solvent remaining in the washed molding being removed by using warm water.
  • the molten polymer is fed into a first inlet at an end of a first manifold and a second inlet at the end of a second manifold on the opposite side of the first inlet.
  • Two slit currents flow together inside the die. It is theorized that due to the absence of flow divergence of the melt inside the manifold, it may be possible to achieve uniform flow distribution within the die. This is said to result in improved thickness uniformity in the transverse direction the film or the sheet.
  • 2004-083866 proposes a method for producing a polyolefin microporous film that includes preparing a gel-like molded product by melting and kneading the polyolefin with a liquid solvent, extruding the molten and kneaded product from a die, simultaneously and biaxially drawing in the machine and vertical directions, subsequently drawing at a higher temperature than that of the simultaneous biaxial drawing to increase anisotropy against the primary drawing.
  • the redrawing is carried out to satisfy both relations: 0 ⁇ lt/ ⁇ 2m ⁇ 10, wherein ⁇ lt denotes a draw ratio of the biaxial drawing in the vertical direction and ⁇ 2m denotes a draw ratio of the redrawing in the machine direction, and 0 ⁇ lm/ ⁇ 2t ⁇ 10, wherein ⁇ lm denotes a draw ratio of the biaxial drawing in the machine direction and ⁇ 2t denotes a draw ratio of the redrawing in the vertical direction.
  • WO 2004/089627 discloses a microporous polyolefin membrane made of polyethylene and polypropylene comprising two or more layers, the polypropylene content being more than 50% and 95% or less by mass in at least one surface layer, and the polyethylene content being 50 to 95% by mass in the entire membrane.
  • WO 2005/113657 discloses a microporous polyolefin membrane having conventional shutdown properties, meltdown properties, dimensional stability and high- temperature strength. The membrane is made using a polyolefin composition comprising (a) composition comprising lower molecular weight polyethylene and higher molecular weight polyethylene, and (b) polypropylene. This microporous polyolefin membrane is produced by a so-called "wet process". - A -
  • a process for producing a microporous membrane includes the steps of combining a polyolefin composition and at least one diluent (e.g., a solvent) to form a mixture (e.g., a polyolefin solution), the polyolefin composition comprising at least a first polyethylene having a crystal dispersion temperature (T Cd ) and polypropylene, extruding the polyolefin solution through an extrusion die to form an extrudate, cooling the extrudate to form a cooled extrudate having a first area, orienting the cooled extrudate in at least a first direction by about one to about ten fold at a temperature of about T Cd +/- 15°C and further orienting the cooled extrudate in at least a second direction by about one to about five fold at a temperature about 10 0 C to about 40°C higher than the temperature employed in the first orienting step to
  • a process for reducing transverse direction film thickness fluctuation in a film or sheet produced from a mixture comprising at least a first polyethylene having a crystal dispersion temperature (T Cd ), a polypropylene and a solvent or diluent.
  • the process includes the steps of extruding the polyolefin solution through an extrusion die to form an extrudate, cooling the extrudate to form a cooled extrudate, orienting the cooled extrudate in at least a first direction by about one to about ten fold at a temperature of about T Cd +/- 15°C and further orienting the cooled extrudate in at least a second direction by about one to about five fold at a temperature about 10°C to about 40°C higher than the temperature employed in the first orienting step.
  • the oriented cooled extrudate is further processed to produce a membrane, utilizing the steps of removing at least a portion of the diluent to form a membrane, optionally stretching the dried membrane to a magnification of from about 1.1 to about 2.5 fold in at least one direction to form a stretched membrane, and heat- setting the membrane product of to form the microporous membrane.
  • a system for reducing transverse direction film thickness fluctuation in a film or sheet produced from a polyolefin solution, the polyolefin solution comprising at least a first polyethylene having a crystal dispersion temperature (T Cd ), a polypropylene and a solvent or diluent is provided.
  • the system includes an extruder for preparing the polyolefin solution, an extrusion die for receiving and extruding the polyolefin solution to form an extrudate, means for cooling the extrudate to form a cooled extrudate, a first stretching machine for orienting the cooled extrudate in at least a first direction by about one to about ten fold at a temperature of about T cd +/- 15°C, a second stretching machine for further orienting the cooled extrudate in at least a second direction by about one to about five fold at a temperature about 10 0 C to about 40°C higher than the temperature employed by said first stretching machine, and a controller for regulating the temperature of the first stretching machine and the temperature of the second stretching machine, wherein the transverse direction film thickness fluctuation of a film or sheet produce by the system is reduced by at least 25%.
  • the first stretching machine is a roll-type stretching machine.
  • the first stretching machine is a tenter-type stretching machine.
  • the second stretching machine is a tenter-type stretching machine.
  • the polyolefin solution includes (i) at least about 5 wt.% high density polyethylene or at least about 6 wt.% high density polyethylene, or at least about 10 wt.% high density polyethylene, or at least about 30 wt.% high density polyethylene, and (ii) at least about 5 wt.% polypropylene or at least about 10 wt.% polypropylene or at least about 30 wt.% polypropylene, and (iii) at least about 4 wt.% ultra high molecular weight polyethylene or at least about 10 wt.% ultra high molecular weight polyethylene, the weight percents being based on the weight of the polyolefin solution.
  • the polyolefin solution includes at least about 30 wt.% high density polyethylene, at least about 30 wt.% polypropylene and at least about 20 wt.% ultra high molecular weight polyethylene, the weight percents being based on the weight of the polyolefin solution.
  • the polyolefin of the polyolefin solution comprises from about 40% to about 100% or from about 20% to about 80% of the first polyethylene resin, the first polyethylene resin having a weight-average molecular weight ("Mw") of from about 2 x 10 5 to about 9 x 10 5 and a molecular weight distribution (“MWD" defined as MWD) of from about 3 to about 50, from about 5% to about 60 % or from about 15% to about 50 % of a polypropylene resin having an Mw of from about 6 x 10 5 to about 4 x 10 6 , an MWD of from about 3 to about 30 and a heat of fusion of 90 J/g or more, and from about 0% to about 40% of a second polyethylene resin having an Mw of from 1 x 10 6 to about 5 x 10 6 , an MWD of from about 3 to about 30, with the percentages based upon the mass of the polyolefin composition.
  • Mw weight-average molecular weight
  • MWD molecular weight distribution
  • the invention relates to a microporous membrane comprising polyethylene and polypropylene and having a thickness fluctuation standard deviation in at least one planar direction of ⁇ 0.7 ⁇ m and a melt down temperature > 150°C.
  • the invention relates to a battery comprising a anode, a cathode, at least one separator located between the anode and the cathode, the separator comprising polyethylene and polypropylene and having a thickness fluctuation standard deviation in at least one planar direction of ⁇ 0.7 ⁇ m and a melt down temperature > 150°C.
  • FIG. 1 is a schematic view of one embodiment of a system for producing a sequential biaxially oriented film or sheet of thermoplastic material, in accordance herewith;
  • FIG. 2 is a schematic view of another embodiment of a system for producing a sequential biaxially oriented film or sheet of thermoplastic material, in accordance herewith.
  • the invention relates to a microporous membrane comprising polyethylene and polypropylene and having an improved balance of properties including improved melt down temperature and improved thickness variation in at least one planar direction. While the presence of polypropylene in the membrane can be advantageous for increasing the membrane's melt down temperature, the use of polypropylene can worsen other membrane properties such as the membrane's thickness fluctuation. It has been discovered that this difficulty can be overcome, as described below, so that a membrane having well-balanced properties can be produced. [0023] Reference is now made to FIGS. 1-2, wherein like numerals are used to designate like parts throughout.
  • System 10 for producing a microporous film or sheet of thermoplastic material is shown.
  • System 10 includes an extruder 12, extruder 12 having a feed hopper 14 for receiving one or more polymeric materials, processing additives, or the like, fed by a line 14.
  • Extruder 12 also receives a nonvolatile diluent (e.g., a solvent, such as paraffin oil) through a solvent feedline 16.
  • a mixture e.g., a polymeric solution
  • the heated mixture is then extruded into a sheet 18 from a die 20 of extruder 12.
  • the extruded sheet 18 is cooled by a plurality of chill rolls 22 to a temperature lower than the gelling temperature, so that the extruded sheet 18 gels.
  • the cooled extrudate 18' passes to a first orientation apparatus 24, which may be a roll-type stretching machine, as shown.
  • the cooled extrudate 18' is oriented with heating in the machine direction (MD) through the use of the roll-type stretching machine 24 and then the cooled extrudate 18' passes to a second orientation apparatus 26, for sequential orientation in at least the transverse direction (TD), to produce a biaxially oriented film or sheet 18".
  • Second orientation apparatus 26 may be a tenter-type stretching machine and may be utilized for further stretching in the MD.
  • the biaxially oriented film or sheet 18" next passes to a solvent extraction device 28 where a readily volatile solvent such as methylene chloride is fed in through line 30.
  • a readily volatile solvent such as methylene chloride
  • the volatile solvent containing extracted diluent is recovered from a solvent outflow line 32.
  • the oriented film or sheet 18" next passes to a drying device 34, wherein the volatile solvent 36 is evaporated from the biaxially oriented film or sheet 18".
  • the biaxially oriented film or sheet 18" next passes to dry orientation device 38 where the dried membrane is stretched to a magnification of from about 1.1 to about 2.5 fold in at least one direction to form a stretched membrane.
  • the biaxially oriented film or sheet 18" next passes to the heat treatment device 44 where the biaxially oriented film or sheet 18" is annealed so as to adjust porosity and remove stress left in the film or sheet 18", after which biaxially oriented film or sheet 18" is rolled up to form product roll 48.
  • FIG. 2 another form of a system 100 for producing a microporous film or sheet of thermoplastic material is shown.
  • System 100 includes an extruder 112, extruder 112 having a feed hopper 115 for receiving one or more polymeric materials, processing additives, or the like, feed by a line 114.
  • extruder 112 also receives a diluent (e.g., a nonvolatile solvent, such as paraffin oil) through a solvent feedline 116.
  • a diluent e.g., a nonvolatile solvent, such as paraffin oil
  • a mixture e.g., a polymeric solution
  • the heated mixture (e.g., polymeric solution) is then extruded into a sheet 118 from a die 120 of extruder 112.
  • the extruded sheet 118 is cooled by a plurality of chill rolls 122 to a temperature lower than the gelling temperature, so that the extruded sheet 118 gels.
  • the cooled extrudate 118' passes to a first orientation apparatus 124, which may be a tenter-type stretching machine, as shown.
  • the cooled extrudate 1 18' is oriented with heating in the machine direction (MD) and/or the transverse direction (TD) and then the cooled extrudate 118' passes to a second orientation apparatus 126, for sequential orientation in the MD and/or TD, to produce an oriented film or sheet 118".
  • Second orientation apparatus 126 may also be a tenter-type stretching machine.
  • the oriented film or sheet 118" next passes to a solvent extraction device 128 where a readily volatile solvent such as methylene chloride is fed in through line 130.
  • the volatile solvent containing extracted diluent is recovered from a solvent outflow line 132.
  • the biaxially oriented film or sheet 118" next passes to a drying device 134, wherein the volatile solvent 136 is evaporated from the biaxially oriented film or sheet 118".
  • the oriented film or sheet 118" next passes to dry orientation device 138 where the dried membrane is stretched to a magnification of from about 1.1 to about 2.5 fold in at least one direction to form a stretched membrane.
  • the oriented film or sheet 18" next passes to the heat treatment device 144 where the oriented film (e.g., biaxially oriented film) or sheet 18" is annealed so as to adjust porosity and remove stress left in the film or sheet 18", after which biaxially oriented film or sheet 118" is rolled up to form product roll 148.
  • the system disclosed herein is useful in forming microporous polyolefin membrane films and sheets.
  • films and sheets have reduced thickness variation in the transverse direction and find particular utility in the critical field of battery separators.
  • the films and sheets disclosed herein provide a good balance of key. properties, including high meltdown temperature, improved surface smoothness and improved electrochemical stability while maintaining high permeability, good mechanical strength and low heat shrinkage with good compression resistance.
  • the microporous membranes disclosed herein exhibit excellent heat shrinkage, melt down temperature and thermal mechanical properties; i.e., reduced maximum shrinkage in the molten state.
  • the invention relates to a first microporous membrane comprising polyethylene and polypropylene and having a thickness fluctuation standard deviation in at least one planar direction of ⁇ 0.7 ⁇ m and a melt down temperature > 150°C, and at least a second membrane (e.g., a coating or layer) in contact with the first membrane.
  • the second membrane is generally microporous and can comprise one or more of, e.g., ceramic, polymer (e.g., polyolefin), etc.
  • the second membrane can be in face-to-face (e.g., planar) contact with the first membrane.
  • Starting materials which are generally combined and used in the form of a polymer composition such as a polyolef ⁇ n composition
  • the finished membrane generally comprises the polymer(s) used to produce the membrane.
  • the selection of a starting material is not critical. In one form, the starting material contains polyethylene and polypropylene.
  • the starting materials contain polypropylene (PP-I) and at least one of (i) a first polyethylene (“PE-I”) having an Mw value ⁇ 1 x 10 6 and (ii) a second polyethylene (“UHMWPE-I”) having an Mw value > 1 x 10 6 .
  • PE-I first polyethylene
  • UHMWPE-I second polyethylene
  • UHMWPE-I can preferably have an Mw in the range of from 1 x 10 6 to about 15 x 10 6 or from 1 x 10 6 to about 5 x 10 6 or from 1.2 x 10 6 to about 3 x 10 6 .
  • the amount of UHMWPE-I in the membrane is in the range of 0 wt.% to about 40 wt.%, or about 1 wt.% to about 30 wt.%, or about 1 wt.% to 20 wt.%, on the basis of total amount of PE-I and UHMWPE-I in the membrane, it is less difficult to obtain a finished membrane having a hybrid structure defined in the later section.
  • UHMWPE-I can be, for example, one or more of (i) an ethylene homopolymer or (ii) a copolymer (random or block) of ethylene one or more of ⁇ -olefins such as propylene, butene-1, pentene-1, hexene-1, 4- methylpentene-1, octene-1, vinyl acetate, methyl methacrylate, and styrene, etc.; and diolefins such as butadiene, 1,5-hexadiene, 1 ,7-octadiene, 1 ,9-decadiene, etc.
  • the amount of comonomer is generally less than 10% by mol based on 100% by mol of the entire copolymer.
  • PP-I is present in the membrane in an amount in the range of about 5 wt.% to about 60 wt.%, or about 30 wt.% to 50 wt.%, or no more than about 60 wt.%, on the basis of the total weight of the microporous film or sheet material.
  • the polypropylene can be, for example, one or more of (i) a propylene homopolymer or (ii) a copolymer (random or block) of propylene and one or more of ⁇ -olefins such as ethylene, butene-1, pentene-1, hexene-1, 4-methylpentene-l, octene-1, vinyl acetate, methyl methacrylate, and styrene, etc.; and diolefins such as butadiene, 1,5-hexadiene, 1,7-octadiene, 1 ,9-decadiene, etc.
  • ⁇ -olefins such as ethylene, butene-1, pentene-1, hexene-1, 4-methylpentene-l, octene-1, vinyl acetate, methyl methacrylate, and styrene, etc.
  • diolefins such as butadiene, 1,5-hexa
  • the polypropylene has one or more of the following properties: (i) the polypropylene has an Mw ranging from about 1 x 10 4 to about 4 x 10 6 , or about 3 x 10 5 to about 3 x 10 6 , or about 6 x 10 5 to about 1.5 x 10 6 , (ii) the polypropylene has an MWD (defined as Mw/Mn) in the range of from about 1.01 to about 100, or about 1.1 to about 50, or about 3 to about 30; (iii) the polypropylene's tacticity is isotactic; (iv) the polypropylene has a heat of fusion of at least about 90 Joules/gram or about 100 J/g to 120 J/g; (v) polypropylene has a melting peak (second melt) of at least about 160°C, (vi) the polypropylene has one or more of the following properties: (i) the polypropylene has an Mw ranging from about 1 x 10 4 to about 4 x 10
  • the polyolefin in the microporous film or sheet material can have an Mw of about 1.5 x 10 6 or less, or in the range of from about 1.0 x 10 5 to about 2.0 x 10 6 or from about 2.0 x 10 5 to about 1.5 x 10 6 in order to obtain a microporous film or sheet having a hybrid structure defined in the later section.
  • PE-I can preferably have an Mw ranging from about 1 x 10 4 to about 9 x 10 5 , or from about 2 x 10 5 to about 8 x 10 5 , and can be one or more of a high-density polyethylene, a medium-density polyethylene, a branched low-density polyethylene, or a linear low-density polyethylene.
  • PE-I can be, for example, one or more of (i) an ethylene homopolymer or (ii) a copolymer (random or block) of ethylene one or more of ⁇ -olefins such as propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-l, octene-1, vinyl acetate, methyl methacrylate, and styrene, etc.; and diolefins such as butadiene, 1,5-hexadiene, 1 ,7-octadiene, 1 ,9-decadiene, etc.
  • the amount of comonomer is generally less than 10% by mol based on 100% by mol of the entire copolymer.
  • the microporous film or sheet has a hybrid structure, which is characterized by a pore size distribution exhibiting relatively dense domains having a main peak in a range of 0.01 ⁇ m to 0.08 ⁇ m and relatively coarse domains exhibiting at least one sub-peak in a range of more than 0.08 ⁇ m to 1.5 ⁇ m or less in the pore size distribution curve.
  • the ratio of the pore volume of the dense domains (calculated from the main peak) to the pore volume of the coarse domains (calculated from the sub-peak) is not critical, and can range, e.g., from about 0.5 to about 49.
  • Mw and MWD of the polyethylene and polypropylene are determined using a High Temperature Size Exclusion Chromatograph, or "SEC", (GPC PL 220, Polymer Laboratories), equipped with a differential refractive index detector (DRI). The measurement is made in accordance with the procedure disclosed in " Macromolecules, Vol. 34, No. 19, pp. 6812-6820 (2001)”. Three PLgel Mixed-B columns available from (available from Polymer Laboratories) are used for the Mw and MWD determination. For polyethylene, the nominal flow rate is 0.5 cm 3 /min; the nominal injection volume is 300 ⁇ L; and the transfer lines, columns, and the DRI detector are contained in an oven maintained at 145 0 C.
  • SEC High Temperature Size Exclusion Chromatograph
  • DRI detector differential refractive index detector
  • the nominal flow rate is 1.0 cm 3 /min; the nominal injection volume is 300 ⁇ L; and the transfer lines, columns, and the DRI detector are contained in an oven maintained at 160°C.
  • the GPC solvent used is filtered Aldrich reagent grade 1,2,4- Trichlorobenzene (TCB) containing approximately 1000 ppm of butylated hydroxy toluene (BHT).
  • TCB was degassed with an online degasser prior to introduction into the SEC. The same solvent is used as the SEC eluent.
  • Polymer solutions were prepared by placing dry polymer in a glass container, adding the desired amount of the TCB solvent, and then heating the mixture at 160 0 C with continuous agitation for about 2 hours.
  • the concentration of polymer solution was 0.25 to 0.75mg/ml.
  • Sample solution are filtered off-line before injecting to GPC with 2 ⁇ m filter using a model SP260 Sample Prep Station (available from Polymer Laboratories).
  • the separation efficiency of the column set is calibrated with a calibration curve generated using a seventeen individual polystyrene standards ranging in Mp ("Mp" being defined as the peak in Mw) from about 580 to about 10,000,000.
  • Mp being defined as the peak in Mw
  • the polystyrene standards are obtained from Polymer Laboratories (Amherst, MA).
  • a calibration curve (logMp vs. retention volume) is generated by recording the retention volume at the peak in the DRI signal for each PS standard and fitting this data set to a 2nd-order polynomial. Samples are analyzed using IGOR Pro, available from Wave Metrics, Inc.
  • the microporous film or sheet material can optionally contain one or more additional polyolefins, identified as the seventh polyolefin, which can be, e.g., one or more of polybutene- 1 , polypentene-1, poly-4-methylpentene-l, polyhexene-1, polyoctene-1, polyvinyl acetate, polymethyl methacrylate, polystyrene and an ethylene ⁇ -olefin copolymer (except for an ethylene-propylene copolymer) and can have an Mw in the range of about 1 x 10 4 to about 4 x 10 6 .
  • additional polyolefins identified as the seventh polyolefin, which can be, e.g., one or more of polybutene- 1 , polypentene-1, poly-4-methylpentene-l, polyhexene-1, polyoctene-1, polyvinyl acetate, polymethyl methacrylate, polystyrene
  • the microporous film or sheet material can further comprise a polyethylene wax, e.g., one having an Mw in the range of about 1 x 10 3 to about 1 x 10 4 .
  • a method for producing a microporous polyolefin membrane comprises the steps of (1) combining (e.g., by melt-blending) a polyolefin composition and at least one diluent (e.g.
  • a membrane-forming solvent to prepare a mixture (e.g., polyolefin solution), (2) extruding the mixture through a die to form an extrudate, (3) cooling the extrudate to form a gel-like sheet (cooled extrudate), (4) sequentially orienting the cooled extrudate through the use of a first orientation or stretching step and a second orientation or stretching step, (5) removing the membrane- forming solvent from the gel-like sheet to form a solvent-removed gel-like sheet, and (6) drying the solvent-removed gel-like sheet in order to form the, microporous membrane.
  • An optional hot solvent treatment step (7) can be conducted between steps (4) and (5), if desired.
  • an optional step (8) of stretching the microporous membrane, an optional heat treatment step (9), an optional cross-linking step with ionizing radiations (10), and an optional hydrophilic treatment step (11), etc. can be conducted. While the invention will be described in terms of a polyolefin composition combined with a membrane-forming solvent to produce a polyolefin solution, which is then extruded, the invention is not limited thereto.
  • the polyolefin composition comprises polyolefin resins as described above that can be combined, e.g., by dry mixing or melt blending with an appropriate diluent to produce the mixture.
  • mixture can contain various additives such as one or more antioxidant, fine silicate powder (pore-forming material), etc., provided these are used in a concentration range that does not significantly degrade the desired properties of the, microporous membrane.
  • the diluent e.g., a membrane-forming solvent
  • a solvent that is liquid at room temperature. While not wishing to be bound by any theory or model, it is believed that the use of a liquid solvent to form the polyolef ⁇ n solution makes it possible to conduct stretching of the gel-like sheet at a relatively high stretching magnification.
  • the membrane-forming solvent can be at least one of aliphatic, alicyclic or aromatic hydrocarbons such as nonane, decane, decalin, p-xylene, undecane, dodecane, liquid paraffin, etc.; mineral oil distillates having boiling points comparable to those of the above hydrocarbons; and phthalates liquid at room temperature such as dibutyl phthalate, dioctyl phthalate, etc.
  • non- volatile liquid solvents such as liquid paraffin can be used, either alone or in combination with other solvents.
  • a solvent which is miscible with polyethylene in a melt blended state but solid at room temperature can be used, either alone or in combination with a liquid solvent.
  • a liquid solvent can include, e.g., stearyl alcohol, ceryl alcohol, paraffin waxes, etc.
  • the viscosity of the liquid solvent is not a critical parameter.
  • the viscosity of the liquid solvent can range from about 30 cSt to about 500 cSt, or from about 30 cSt to about 200 cSt, at 25°C.
  • the resins, etc., used to produce to the polyolefin composition are melt-blended in, e.g., a double screw extruder or mixer.
  • a conventional extruder or mixer or mixer-extruder
  • a double-screw extruder can be used to combine the resins, etc., to form the polyolefin composition.
  • the membrane- forming solvent can be added to the polyolefin composition (or alternatively to the resins used to produce the polyolefin composition) at any convenient point in the process.
  • the solvent can be added to the polyolefin composition (or its components) at any of (i) before starting melt-blending, (ii) during melt blending of the first polyolefin composition, or (iii) after melt-blending, e.g., by supplying the membrane-forming solvent to the melt-blended or partially melt-blended polyolefin composition in a second extruder or extruder zone located downstream of the extruder zone used to melt-blend the polyolefin composition.
  • the melt-blending temperature is not critical.
  • the melt-blending temperature of the polyolefin solution can range from about 10°C higher than the melting point T m i of the polyethylene in the first resin to about 120°C higher than T ml .
  • such a range can be represented as T ml + 10 0 C to T ml + 120 0 C.
  • the melt-blending temperature can range from about 140 0 C to about 250 0 C, or from about 170 0 C to about 240 0 C.
  • the screw parameters are not critical.
  • the screw can be characterized by a ratio L/D of the screw length L to the screw diameter D in the double-screw extruder, which can range, for example, from about 20 to about 100 or from about 35 to about 70.
  • L/D the screw length L to the screw diameter D in the double-screw extruder
  • melt-blending can be more difficult
  • L/D is more than about 100
  • faster extruder speeds might be needed to prevent excessive residence time of the polyolefin solution in the double-screw extruder, which can lead to undesirable molecular weight degradation.
  • the cylinder (or bore) of the double-screw extruder can have an inner diameter of in the range of about 40 mm to about 100 mm, for example.
  • the amount of the polyolefin composition in the polyolefin solution is not critical. In one form, the amount of polyolefin composition in the polyolefin solution can range from about 1 wt.% to about 75 wt.%, based on the weight of the polyolefin solution, for example from about 20 wt.% to about 70 wt.%.
  • a monolayer extrusion die can be used to form an extrudate.
  • the extrusion die is connected to an extruder, where the extruder contains the polyolefin solution.
  • the die gap is generally not critical.
  • the extrusion die can have a die gap of about 0.1 mm to about 5 mm.
  • Die temperature and extruding speed are also non-critical parameters.
  • the die can be heated to a die temperature ranging from about 140°C to about 250°C during extrusion.
  • the extruding speed can range, for example, from about 0.2 m/minute to about 15 m/minute.
  • a gel-like sheet can be obtained by cooling, for example. Cooling rate and cooling temperature are not particularly critical. For example, the gel-like sheet can be cooled at a cooling rate of at least about 50°C/minute until the temperature of the gel- like sheet (the cooling temperature) is approximately equal to the gel-like sheet's gelatin temperature (or lower). In one form, the extrudate is cooled to a temperature of about 25°C or lower in order to form the gel-like sheet. [0054] In one form, the membrane-forming solvent is removed (or displaced) from the gel-like sheet in order to form a solvent-removed gel-like sheet.
  • a displacing (or “washing") solvent can be used to remove (wash away, or displace) the first and second membrane-forming solvents.
  • the choice of washing solvent is not critical provided it is capable of dissolving or displacing at least a portion of the first and/or second membrane-forming solvent.
  • Suitable washing solvents include, for instance, one or more of volatile solvents such as saturated hydrocarbons such as pentane, hexane, heptane, etc.; chlorinated hydrocarbons such as methylene chloride, carbon tetrachloride, etc.; ethers such as diethyl ether, dioxane, etc.; ketones such as methyl ethyl ketone, etc.; linear fluorocarbons such as trifluoroethane, C 6 Fi 4 , C 7 F] 6 , etc.; cyclic hydrofluorocarbons such as C 5 H 3 F 7 , etc.; hydrofluoroethers such as C 4 F 9 OCH 3 , C 4 F 9 OC 2 Hs, etc.; and perfluoroethers such as C 4 F 9 OCF 3 , C 4 F 9 O C 2 H 5 , etc.
  • volatile solvents such as saturated hydrocarbons such as pentane, hexane, heptane
  • the method for removing the membrane-forming solvent is not critical, and any method capable of removing a significant amount of solvent can be used, including conventional solvent-removal methods.
  • the gel-like sheet can be washed by immersing the sheet in the washing solvent and/or showering the sheet with the washing solvent.
  • the amount of washing solvent used is not critical, and will generally depend on the method selected for removal of the membrane-forming solvent.
  • the membrane-forming solvent is removed from the gel-like sheet (e.g., by washing) until the amount of the remaining membrane-forming solvent in the gel-like sheet becomes less than 1 wt.%, based on the weight of the gel-like sheet.
  • the solvent-removed gel-like sheet obtained by removing the membrane-forming solvent is dried in order to remove the washing solvent.
  • Any method capable of removing the washing solvent can be used, including conventional methods such as heat-drying, wind-drying (moving air), etc.
  • the temperature of the gel-like sheet during drying i.e., drying temperature
  • the drying temperature can be equal to or lower than the crystal dispersion temperature T C(1 .
  • T Cd is the lower of the crystal dispersion temperature T c ⁇ n of the polyethylene in the first resin and the crystal dispersion temperature T Cd2 of the polyethylene in the second resin.
  • the drying temperature can be at least 5°C below the crystal dispersion temperature T Cd .
  • the crystal dispersion temperature of the polyethylene can be determined by measuring the temperature characteristics of the kinetic viscoelasticity of the polyethylene according to ASTM D 4065. In one form, the polyethylene has a crystal dispersion temperature in the range of about 90°C to about 100°C. [0057] Although it is not critical, drying can be conducted until the amount of remaining washing solvent is about 5 wt.% or less on a dry basis, i.e., based on the weight of the dry microporous polyolefin membrane. In another form, drying is conducted until the amount of remaining washing solvent is about 3 wt.% or less on a dry basis.
  • the gel-like sheet Prior to the step of removing the membrane-forming solvents, the gel-like sheet is stretched (i.e., oriented) in at least a first step and a second step, sequentially, in order to obtain a stretched, gel-like sheet.
  • the stretching can be accomplished by one or more of tenter- stretching, roller-stretching, or inflation stretching (e.g., with air).
  • the stretching can be conducted monoaxially (i.e., in either the machine or transverse direction) or biaxially (both the machine and transverse direction).
  • the stretching can be simultaneous biaxial stretching, sequential stretching along one planar axis and then the other (e.g., first in the transverse direction and then in the machine direction), or multistage stretching (for instance, a combination of the simultaneous biaxial stretching and the sequential stretching).
  • the first stretching magnification is not critical.
  • the first stretching magnification in at least one lateral (e.g., planar, when the membrane is flat) direction of the extrudate) can be, e.g., about 1.5 fold or more, or about 1.5 to about 10 fold.
  • the linear stretching magnification can be, e.g., about 1.5 fold or more, or about 1.5 fold to about 16 fold in each of the stretching directions.
  • the second stretching magnification in at least one lateral (e.g., planar, when the membrane is flat) direction of the extrudate) can be, e.g., about 1.5 fold or more, or about 1.5 to about 10 fold.
  • the linear stretching magnification can be, e.g., about 1.5 fold or more, or about 1.5 fold to about 16 fold in each of the stretching directions.
  • the total stretching magnification resulting from the first and second stretching generally results in an increase in membrane area of 10 fold or more, e.g., in the range of 15 fold to 50 fold, such as 20 fold to 30 fold. In an embodiment, the total stretching magnification resulting from the first and second stretching is 25 fold in area.
  • the first and second stretching steps can be called "wet" stretching steps to distinguish them from dry orientation steps that are conducted after the diluent is removed.
  • the temperature of the gel-like sheet during the first orientation or stretching step can be about (T m + 10°C) or lower, or optionally in a range that is higher than T ct j - 15°C but lower than T Cd + 15°C (or lower than T m , wherein T m is the lesser of the melting point T ml of the polyethylene in the first resin and the melting point T m2 of the polyethylene in the second resin).
  • the temperature of the gel-like sheet during the first orientation or stretching step can be about T Cd +/- 15°C, or about T Cd - 10°C to about T cd + 10°C, or about 90 0 C to about 100°C.
  • the temperature of the gel-like sheet during the second orientation or stretching step can be about 10 0 C to about 40 0 C higher than the temperature employed in the first orientation or stretching step. In one form, the temperature of the gel-like sheet during the first orientation or stretching step can be about 115°C to about 130 0 C, or about 120 0 C to about 125°C.
  • the stretching makes it easier to produce a relatively high-mechanical strength microporous polyolefin membrane with a relatively large pore size. Such microporous membranes are believed to be particularly suitable for use as battery separators.
  • the gel-like sheet can be treated with a hot solvent. When used, it is believed that the hot solvent treatment provides the fibrils (such as those formed by stretching the gel-like sheet) with a relatively thick leaf-vein- like structure. The details of this method are described in WO 2000/20493.
  • the dried microporous membrane can be stretched, at least monoaxially.
  • the stretching method selected is not critical, and conventional stretching methods can be used such as by a tenter method, etc.
  • the stretching of the dry microporous polyolefin membrane can be called dry-stretching, re-stretching, or dry-orientation.
  • the temperature of the dry microporous membrane during stretching is not critical.
  • the dry stretching temperature is approximately equal to the melting point T m or lower, for example in the range of from about the crystal dispersion temperature T c ⁇ j to the about the melting point T m .
  • the dry stretching temperature ranges from about 90°C to about 135°C, or from about 95°C to about 130°C.
  • the stretching magnification is not critical.
  • the stretching magnification of the microporous membrane can range from about 1.1 fold to about 2.5 or about 1.1 to about 2.0 fold in at least one lateral (planar) direction.
  • the membrane relaxes (or shrinks) in the direction(s) of stretching to achieve a final magnification of about 1.0 to about 2.0 fold compared to the size of the film at the start of the dry orientation step.
  • the dried microporous membrane can be heat-treated.
  • the heat treatment comprises heat-setting and/or annealing.
  • heat-setting it can be conducted using conventional methods such as tenter methods and/or roller methods.
  • the temperature of the dried microporous polyolefin membrane during heat-setting i.e., the "heat-setting temperature" can range from the T cd to about the T m , or from about 120°C to about 130°C.
  • Annealing differs from heat-setting in that it is a heat treatment with no load applied to the microporous polyolefin membrane.
  • the choice of annealing method is not critical, and it can be conducted, for example, by using a heating chamber with a belt conveyer or an air-floating-type heating chamber. Alternatively, the annealing can be conducted after the heat-setting with the tenter clips slackened.
  • the temperature of the microporous polyolefin membrane during annealing can range from about the melting point T m or lower, from about 60 0 C to (T m - 10°C), or in a range of from about 60 0 C to (T m - 5°C).
  • the microporous polyolefin membrane can be cross-linked (e.g., by ionizing radiation rays such as a-rays, (3 -rays, 7-rays, electron beams, etc.) or can be subjected to a hydrophilic treatment (i.e., a treatment which makes the microporous polyolefin membrane more hydrophilic (e.g., a monomer-grafting treatment, a surfactant treatment, a corona-discharging treatment, etc.)).
  • a hydrophilic treatment i.e., a treatment which makes the microporous polyolefin membrane more hydrophilic (e.g., a monomer-grafting treatment, a surfactant treatment, a corona-discharging treatment, etc.)
  • the membrane's thickness (average thickness, as described below) is generally in the range of from about 1 ⁇ m to about 100 ⁇ m, e.g., from about 5 ⁇ m to about 30 ⁇ m.
  • the thickness of the microporous membrane can be measured by a contact thickness meter at 1 cm longitudinal intervals over the width of 20 cm, and then averaged to yield the membrane thickness.
  • Thickness meters such as the Litematic available from Mitsutoyo Corporation are suitable. This method is also suitable for measuring thickness fluctuation and thickness variation after heat compression, as described below.
  • Non-contact thickness measurements are also suitable, e.g., optical thickness measurement methods.
  • the multi-layer microporous membrane has a thickness ranging from about 3 ⁇ m to about 200 ⁇ m, or ' about 5 ⁇ m to about 50 ⁇ m.
  • the membrane is a monolayer membrane comprising:
  • the microporous membrane has one or more of the following properties.
  • the membrane When the porosity is less than 25%, the microporous membrane generally does not exhibit the desired air permeability necessary for use as a battery separator. When the porosity exceeds 80%, it is more difficult to produce a battery separator of the desired strength, which can increase the likelihood of internal electrode short-circuiting.
  • the membrane has a porosity > 25%, e.g., in the range of about 25% to about 80%, or 30% to 60%. The membrane's porosity is measured conventionally by comparing the membrane's actual weight to the weight of an equivalent non-porous membrane of the same composition (equivalent in the sense of having the same length, width, and thickness).
  • the membrane's normalized air permeability of the microporous membrane ranges from about 20 seconds/100 cm 3 to about 400 seconds/100 cm 3 , it is less difficult to form batteries having the desired charge storage capacity and desired cyclability.
  • the air permeability is less than about 20 seconds/100 cm 3 , it is more difficult to produce a battery having the desired shutdown characteristics, particularly when the temperature inside the battery is elevated.
  • the membrane's normalized air permeability is in the range of from about 100 seconds/100 cm 3 to about 300 seconds/100 cm 3 .
  • the pin puncture strength (normalized to a 20 ⁇ m membrane thickness) is the maximum load measured when the microporous membrane is pricked with a needle 1 mm in diameter with a spherical end surface (radius R of curvature: 0.5 mm) at a speed of 2 mm/second.
  • the pin puncture strength is preferably 3,500 mN/20 ⁇ m or more, for example, 4,000 mN/20 ⁇ m or more.
  • the membrane has a pin puncture strength in the range of 4,000 to 5,000 mN/20 ⁇ m.
  • Pin puncture strength is defined as the maximum load measured when a microporous membrane having a thickness of T 1 is pricked with a needle of 1 mm in diameter with a spherical end surface (radius R of curvature: 0.5mm) at a speed of 2mm/second.
  • the tensile strength of the microporous membrane is at least about 60,000 kPa in both longitudinal and transverse directions, it is less difficult to produce a battery of the desired mechanical strength.
  • the tensile strength is preferably about 80,000 kPa or more, for example about 100,000 kPa or more.
  • Tensile strength is measured in MD and TD according to ASTM D-882A. In an embodiment, the membrane's MD and TD tensile strength are each in the range of 80,000 kPa to 200,000 kPa.
  • the membrane's heat shrinkage ratio is preferably 12% or less or 10% or less in MD and TD.
  • the membrane's MD 105°C heat shrinkage can be ⁇ 3.5%, e.g., in the range of 0.5% to 3.5%; and the 105°C TD heat shrinkage can be ⁇ 5%, e.g., in the range of 1% to 5%.
  • the MD and TD heat shrinkage ratios are measured three times when exposed to 105°C for 8 hours, and averaged to determine the heat shrinkage ratio.
  • the membrane's heat shrinkage in orthogonal planar directions (e.g., MD or TD) at 105°C is measured as follows:
  • the membrane's 105°C MD and TD heat shrinkages are each in the range of 1% to 5%.
  • G. Thickness Fluctuation of 1.0 ⁇ m or Less When the thickness fluctuation of a battery separator exceeds 1.0 ⁇ m, it is more difficult to produce a battery with appropriate protection against internal short circuiting. Thickness fluctuation is expressed as a standard deviation. It is measured as follows: The thickness of the microporous membrane is measured by a contact thickness meter at 1 cm intervals in the area of 10 cm x 10 cm of the membrane, to provide a membrane thickness at 100 data points.
  • the membrane's thickness fluctuation in at least one planar direction is ⁇ 0.7 ⁇ m, e.g., in the range of 0.25 ⁇ m to 0.65 ⁇ m.
  • H. Puncture Strength Fluctuation of 10.0 mN or Less, e.g., 9 mN or less When the puncture strength fluctuation of a battery separator exceeds 10 mN, it is more difficult to produce a battery having appropriate durability and reliability.
  • the membrane's pin puncture strength fluctuation is in the range of 5 mN to 9 mN.
  • the melt down temperature can range from about 150°C to about 190 0 C.
  • the melt down temperature can be > 160°C, e.g., in the range of from 160°C to 190°C, e.g., from 17O 0 C to 190°C.
  • Melt down temperature is measured by the following procedure: A rectangular sample of 3 mm x 50 mm is cut out of the microporous membrane such that the long axis of the sample is aligned with the transverse direction of the microporous membrane as it is produced in the process and the short axis is aligned with the machine direction.
  • the sample is set in a thermomechanical analyzer (TMA/SS6000 available from Seiko Instruments, Inc.) at a chuck distance of 10 mm, i.e., the distance from the upper chuck to the lower chuck is 10mm.
  • the lower chuck is fixed and a load of 19.6 mN applied to the sample at the upper chuck.
  • the chucks and sample are enclosed in a tube which can be heated. Starting at 30 0 C, the temperature inside the tube is elevated at a rate of 5°C/minute, and sample length change under the 19.6 mN load is measured at intervals of 0.5 second and recorded as temperature is increased. The temperature is increased to 200 0 C.
  • the melt down temperature of the sample is defined as the temperature at which the sample breaks.
  • the membrane's melt down temperature is in the range of about 165°C to about 200 0 C, such as about 170 0 C to about 195°C.
  • J. Maximum Shrinkage in Molten State of 30% or Less The microporous membrane can exhibit a maximum shrinkage in the molten state (about 140°C) of about 30% or less, preferably about 25% or less. In an embodiment, the membrane's maximum shrinkage in the molten state is in the range of 10% to 25%. Maximum shrinkage in the molten state in a planar direction of the membrane is measured by the following procedure.
  • the sample length measured in the temperature range of from 135°C to 145°C are recorded.
  • the maximum shrinkage in the molten state is defined as the sample length between the chucks measured at 23 °C (Ll equal to 10mm) minus the minimum length measured generally in the range of about 135°C to about 145°C (equal to L2) divided by Ll, i.e., [Ll-L2]/Ll*100%.
  • the rectangular sample of 3 mm x 50 mm used is cut out of the microporous membrane such that the long axis of the sample is aligned with the transverse direction of the microporous membrane as it is produced in the process and the short axis is aligned with the machine direction.
  • MD maximum shrinkage the rectangular sample of 3 mm x 50 mm used is cut out of the microporous membrane such that the long axis of the sample is aligned with the machine direction of the microporous membrane as it is produced in the process and the short axis is aligned with the transverse direction.
  • the thickness variation ratio after heat compression at 90°C under a pressure of 2.2 MPa for 5 minutes is generally 20% or less per 100% of the thickness before compression, e.g., ⁇ 10%.
  • Batteries comprising microporous membrane separators with a thickness variation ratio of 20% or less (e.g., in the range of 5% to 10%) have suitably large capacity and good cyclability.
  • Thickness variation after heat compression is measured by subjecting the membrane to a compression of 2.2 MPa (22 kgf/cm 2 ) in the thickness direction for five minutes while the membrane is exposed to a temperature of 90 0 C.
  • the membrane's thickness variation ratio is defined as the absolute value of (average thickness after compression - average thickness before compression) / (average thickness before compression) x 100. The result is expressed as an absolute value.
  • the microporous membranes disclosed herein when heat-compressed at 90°C under pressure of 2.2 MPa for 5 minutes, have an air permeability (as measured according to JIS P8117) of about 1000 sec/100 cm 3 or less, e.g., 600 sec/100 cm 3 , such as from about 100 to about 600 sec/ 100 cm . Batteries using such membranes have suitably large capacity and cyclability.
  • the air permeability after heat compression may be, for example, 700 sec/100 cm 3 or less. Air permeability after heat compression is measured according to JIS P8117 after the membrane is subjected to a compression of 2.2 MPa (22 kgf/cm 2 ) in the thickness direction for five minutes while the membrane is exposed to a temperature of 90°C.
  • Electrolytic Solution Absorption Speed of a Battery of 3.0 or More Compared to Comparative Example 1 it is desired that the electrolytic solution absorption speed of the battery should be 2.5 or more (e.g., 3.0 or more).
  • Electrolytic solution absorption speed is measured as follows: Using a dynamic surface tension measuring apparatus (DCAT21 with high-precision electronic balance, available from Eko Instruments Co., Ltd.), a microporous membrane sample is immersed in an electrolytic solution for 600 seconds (electrolyte: 1 mol/L of LiPF 6 , solvent: ethylene carbonate/dimethyl carbonate at a volume ratio of 3/7) kept at 18°C, to determine an electrolytic solution absorption speed by the formula of [weight (in grams) of microporous membrane after immersion / weight (in grams) of microporous membrane before immersion].
  • DCAT21 with high-precision electronic balance available from Eko Instruments Co., Ltd.
  • the electrolytic solution absorption speed of the membrane is expressed by a relative value, assuming that the electrolytic solution absorption rate in the microporous membrane of Comparative Example 1 is 1.
  • a membrane having a relatively high electrolytic solution absorption speed e.g., > 2.5
  • the membrane has an electrolytic solution absorbtion speed > 3.5, e.g., in the range of 3.5 to 8.
  • EXAMPLE 1 Dry-blended were 99.8 parts by mass of a polyolefin composition comprising 20% by mass of ultra-high-molecular-weight polyethylene (UHMWPE) having an Mw of 1.9 x 10 6 , an MWD of 5.09, a melting point (T m ) of 135°C, and a crystal dispersion temperature (T Cd ) of 100°C, 50% by mass of high-density polyethylene (HDPE) having a Mw of 5.6 x 10 5 and MWD of 4.05, T m of 135°C, and T Cd of 100°C, and 30% by mass of a polypropylene (PP) having a Mw of 6.6 x 10 5 and MWD of 11.4, and a heat of fusion of 103.3, and 0.2 parts by mass of tetrakis [methylene-3 -(3,5-ditertiary-butyl-4-hydroxy
  • the polyolefin composition had a MWD of 8.6, a T m of 135°C, and T Cd of 100°C.
  • the polyolefin solution was supplied from its double-screw extruder to a monolayer-sheet-forming T-die at 210°C, to form an extrudate.
  • the extrudate was cooled while passing through cooling rolls controlled at 15°C, to form a gel-like sheet.
  • a first tenter-stretching machine the gel-like sheet was biaxially stretched at 100.0°C, to 2 fold in both machine and transverse directions.
  • Using a second tenter- stretching machine the gel-like sheet was again biaxially stretched, this time at 120.0°C, to 2.5, fold in both machine and transverse directions.
  • the stretched gel-like sheet was fixed to an aluminum frame of 20 cm x 20 cm, and immersed in a bath of methylene chloride controlled at a temperature of 25°C to remove the liquid paraffin with a vibration of 100 rpm for 3 minutes.
  • the resulting membrane was air-cooled at room temperature.
  • the dried membrane was re-stretched by a batch-stretching machine to a magnification of 1.4 fold in a transverse direction at 125°C.
  • the re-stretched membrane which remained fixed to the batch-stretching machine, was heat-set at 125°C for 10 minutes to produce a microporous polyolefin membrane.
  • Example 1 was repeated except that the temperature of the second wet stretching of the gel-like sheet was conducted at 125 °C.
  • Example 1 was repeated except that the magnification of the first wet stretching of the gel-like sheet was 5 fold in a machine direction and the magnification of the second wet stretching of the gel-like sheet was 5 fold in a transverse direction. [00103] There was obtained a microporous membrane of polypropylene having the characteristic properties as shown in Table 1.
  • EXAMPLE 4 [00104] Example 1 was repeated except that there was no re-stretching of the dried membrane prior to heat-setting. Another exception from Example 1 for this Example 4 was that the heat setting temperature was 126°C.
  • Example 1 was repeated except that the polyolefin composition included
  • This polyolefin composition contains no second polyethylene resin, [00107] There was obtained a microporous membrane of polypropylene having the characteristic properties as shown in Table 1.
  • Example 1 was repeated except that the polyolefin composition included
  • Example 1 30% by mass of a polypropylene resin having an Mw of 1.1 x 10 6 , an MWD of 5.0, and a heat of fusion of 114.0 J/g.
  • Another exception from Example 1 for this Example 6 is that the heat setting temperature was 126°C.
  • Example 6 was repeated except that the temperature of the second wet stretching of the gel-like sheet was 125°C.
  • Example 1 was repeated except that the polyolefin composition employed included 72% by mass of the first polyethylene resin and 8% by mass of the polypropylene resin and 20% by mass of the second polyethylene resin having an Mw of 2 x lO 6 and MWD of 8.
  • COMPARATIVE EXAMPLE 1 Dry-blended were 99.8 parts by mass of a polyolefin composition comprising 20% by mass of ultra-high-molecular-weight polyethylene (UHMWPE) having an Mw of 1.9 x 10 6 , an MWD of 5.09, a melting point (T m ) of 135°C, and a crystal dispersion temperature (T Cd ) of 100°C, and 80% by mass of high-density polyethylene (HDPE) having a Mw of 5.6 x 10 5 and MWD of 4.05, T m of 135°C, and T ed of 100°C, and 0.2 parts by mass of tetrakis [methylene-3 -(3,5-ditertiary-butyl-4- hydroxyphenyl)-propionate] methane as an antioxidant.
  • UHMWPE ultra-high-molecular-weight polyethylene
  • T m melting point
  • T Cd crystal dispersion temperature
  • HDPE high
  • the polyolefin composition had an MWD of 8.6, a T m of 135°C, and T cd of 100 0 C.
  • T m a T m of 135°C
  • T cd 100 0 C.
  • Thirty parts by mass of the resultant mixture was charged into a strong- blending double-screw extruder having an inner diameter of 58 mm and L/D of 52.5, and 70 parts by mass of liquid paraffin [50 cst (40 0 C)] was supplied to the double-screw extruder via a side feeder. Melt-blending was conducted at 210 0 C and 200 rpm to prepare a first polyolefin solution.
  • the polyolefin solution was supplied from its double-screw extruder to a monolayer-sheet-forming T-die at 210 0 C, to form an extrudate.
  • the extrudate was cooled while passing through cooling rolls controlled at 0 0 C, to form a gel-like sheet.
  • the gel-like sheet was biaxially stretched at 115.0 0 C, to 5 fold in both machine and transverse directions.
  • the stretched gel-like sheet was fixed to an aluminum frame of 20 cm x 20 cm, and immersed in a bath of methylene chloride controlled at a temperature of 25°C to remove the liquid paraffin with a vibration of 100 rpm for 3 minutes.
  • the resulting membrane was air-cooled at room temperature.
  • the dried membrane was not re- stretched for this Example.
  • the membrane was fixed to the batch-stretching machine, and was heat-set at 126.8°C for 10 minutes to produce a microporous polyolefin membrane.
  • the resulting oriented membrane was washed with methylene chloride to remove residual liquid paraffin, followed by drying.
  • Example 1 was repeated except that the gel-like sheet was biaxially stretched at 115.0 0 C, to 5 fold in both the machine and transverse directions. Another exception from Example 1 for this Comparative Example was that the heat setting temperature was 127.5°C.
  • Example 1 was repeated except that the first stretching temperature of the gel-like sheet was 115.0°C. Another exception from Example 1 employed for this
  • Comparative Example was that the heat setting temperature was 127.0°C.
  • Example 1 was repeated except that the first stretching temperature of the gel-like sheet was conducted at 120.0 0 C, and the second stretching temperature was conducted at 100.0°C. Another exception from Example 1 for this Comparative Example was that the heat setting temperature was 126.5°C for polyolefin composition.
  • Example 1 was repeated except that the polyolefin composition employed included 20% by mass of the first polyethylene resin and 10% by mass of the second polyethylene resin. The gel-like sheet was broken in stretching.
  • Example 1 was repeated except that the polyolefin composition employed included 20% by mass of the first polyethylene resin and 30% by mass of the polypropylene resin and 50% by mass of the second polyethylene resin.
  • Example 1 was repeated except that the first gel-like sheet was biaxially stretched at 100.0°C to 1.25 fold in both machine and transverse directions, and, likewise, the sheet was again biaxially stretched this time at 120.0°C to 4 fold in both machine and transverse directions.
  • Example 1 was repeated except that the first gel-like sheet was biaxially stretched at 100.0°C to 1.25 fold in both machine and transverse directions, and, likewise, the sheet was again biaxially stretched this time at 120.0°C to 4 fold in both machine and transverse directions.
  • Table 2 There was obtained a microporous membrane of polypropylene having the characteristic properties as shown in Table 2.
  • Example 1 was repeated except that the polyolefin composition employed included 30% by mass of a polypropylene resin having an Mw of 2.5 x 10 5 , an MWD of 3.5, and a heat of fusion of 69.2 J/g.
  • Example 1 was repeated except that the polyolefin composition employed included 30% by mass of a polypropylene resin having an Mw of 1.6 x 10 6 , an MWD of
  • a system for reducing transverse direction film thickness fluctuation in a film or sheet produced from a polyolefin solution comprising at least a first polyethylene having a crystal dispersion temperature (T Cd ), a polypropylene and a solvent or diluent, the system comprising:
  • a second stretching machine for further orienting the cooled extrudate in at least a second direction by about one to about five fold at a temperature about 10°C to about 4O 0 C higher than the temperature employed by said first stretching machine to a second area at least ten fold larger than the first area;

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Cell Separators (AREA)
  • Manufacture Of Porous Articles, And Recovery And Treatment Of Waste Products (AREA)

Abstract

L'invention concerne une membrane microporeuse ayant un équilibre amélioré de propriétés importantes telles que la température de fusion et les fluctuations d'épaisseur. L'invention concerne également un système et un procédé pour produire une telle membrane, l'utilisation d'une telle membrane comme film séparateur de batterie, des batteries contenant une telle membrane, et l'utilisation de ces batteries comme source d'alimentation dans, par exemple, les véhicules électriques et électriques hybrides.
PCT/JP2008/073936 2007-12-31 2008-12-25 Membrane microporeuse, procédé pour produire cette membrane et utilisation de cette membrane WO2009084719A1 (fr)

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CN104530521A (zh) * 2014-12-11 2015-04-22 郑州大学 一种制备具有隔离结构的导电高分子复合材料的方法
CN106103556A (zh) * 2014-03-24 2016-11-09 东丽电池隔膜株式会社 微多孔塑料膜的制造方法
WO2017152731A1 (fr) * 2016-03-07 2017-09-14 上海恩捷新材料科技股份有限公司 Procédé de préparation d'un séparateur pour batterie lithium-ion
KR101831069B1 (ko) 2015-11-13 2018-02-21 스미또모 가가꾸 가부시키가이샤 필름 제조 방법 및 필름 세정 장치
CN108079794A (zh) * 2017-12-25 2018-05-29 南京航空航天大学 一种超高分子量聚乙烯微孔膜的制备方法
WO2019210535A1 (fr) * 2018-05-04 2019-11-07 上海恩捷新材料科技股份有限公司 Membrane poreuse pour le traitement d'eau et procédé de préparation associé

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WO2010114672A1 (fr) 2009-03-30 2010-10-07 Tonen Chemical Corporation Membranes microporeuses, procédés de fabrication associés, et utilisation desdites membranes en tant que film séparateur de batteries
JP2014238958A (ja) * 2013-06-07 2014-12-18 オートモーティブエナジーサプライ株式会社 非水系電池
US9722229B2 (en) * 2013-09-20 2017-08-01 Ford Global Technologies, Llc Electric vehicle battery attachment assembly and method
WO2016132810A1 (fr) * 2015-02-20 2016-08-25 東レバッテリーセパレータフィルム株式会社 Procédé de production d'une feuille plastique microporeuse
CN109997247B (zh) * 2016-11-17 2022-03-11 香港科技大学 纳米多孔超高分子量聚乙烯薄膜
JP7055662B2 (ja) * 2017-03-03 2022-04-18 住友化学株式会社 フィルム製造装置およびフィルム製造方法
CN113263747B (zh) * 2021-05-25 2022-02-01 四川大学 一种大面积超高分子量聚乙烯超薄膜及其制备方法

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Cited By (9)

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Publication number Priority date Publication date Assignee Title
CN106103556A (zh) * 2014-03-24 2016-11-09 东丽电池隔膜株式会社 微多孔塑料膜的制造方法
CN106103556B (zh) * 2014-03-24 2019-06-07 东丽株式会社 微多孔塑料膜的制造方法及微多孔塑料膜的制造装置
CN104530521A (zh) * 2014-12-11 2015-04-22 郑州大学 一种制备具有隔离结构的导电高分子复合材料的方法
KR101831069B1 (ko) 2015-11-13 2018-02-21 스미또모 가가꾸 가부시키가이샤 필름 제조 방법 및 필름 세정 장치
WO2017152731A1 (fr) * 2016-03-07 2017-09-14 上海恩捷新材料科技股份有限公司 Procédé de préparation d'un séparateur pour batterie lithium-ion
US11101524B2 (en) 2016-03-07 2021-08-24 Shanghai Energy New Materials Technology Co., Ltd. Method for preparing lithium-ion battery separator
CN108079794A (zh) * 2017-12-25 2018-05-29 南京航空航天大学 一种超高分子量聚乙烯微孔膜的制备方法
WO2019210535A1 (fr) * 2018-05-04 2019-11-07 上海恩捷新材料科技股份有限公司 Membrane poreuse pour le traitement d'eau et procédé de préparation associé
US11325074B2 (en) 2018-05-04 2022-05-10 Shanghai Energy New Materials Technology Co., Ltd. Porous membrane for water treatment and method for preparing the same

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